This invention relates to an automatic transformation of a logic circuit, and more particularly to a circuit transformation method and logic design system for optimally transforming a function description or logic circuit into a logically equivalent circuit for a specific technology.
A conventional circuit automatic transformation system utilizes a method in which a portion coinciding with a predefined input pattern is detected from a circuit before transformation, and is replaced directly with a corresponding output pattern according to a given condition, such as the fan-out number of the output terminal (mentioned, for example, in the Collected Papers of the 30th National Convention of Information Processing Society of Japan, pp. 1923-1926, 1985). Furthermore, in a system using a knowledge base (that is, rule base), a rule description system for describing the preliminary condition for activating the rule in the condition part of the rule, and describing the operation (that is, the action) on the circuit when that rule is activated in the conclusion part is widely employed. An apparatus of this sort is disclosed, for example, in the Japanese Laid-open Patent No. 59-168545.
In this conventional example, however, considerations are not given to the simplification of the circuit transformation rule, the efficiency of the transformation rule making, its ease of operation, and the efficiency of circuit transformation processing, and the following enumerated problems, among others, exist.
(1) It is necessary to make many transformation rules differing only in part, such as the condition part and conclusion part of the transformation rule.
(2) Unlike the transformation rule possessed by the designer, it is necessary to describe, in an unnatural form, how to change the circuit, being conscious of the deduction mechanism, when describing the conclusion part of the rule.
(3) In order to realize an advanced transformation from a comprehensive viewpoint conducted by a skilled designer, the description quantity per rule is enormous, and the number of rules is tremendous, which makes actual realization difficult.
(4) From the viewpoint of transformation processing efficiency, there are many transformation rules similar in the condition part, the inference efficiency is very poor, and a lengthy processing time is needed for transformation.
(5) When divising and describing a transformation rule in plural rules, wasteful accesses addition of intermediate data to the description part for working (working memory), retrieval and deletion increase, and the efficiency of inference processing is extremely poor.